JPH09172215A - Wavelength selection method in tunable laser and laser oscillator capable of wavelength selection in tunable laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable selecting the wavelength of an output laser light without installing mechanically movable parts, miniaturize the whole equipment, and stabilize wavelength selecting function, by constituting a laser resonator only for a beam component diffracted in a specified direction by a photoacoustic optical crystal of double refraction. SOLUTION: In a laser oscillator, a laser resonator is constituted of an output side mirror 112 having specified transparency and a total reflection mirror 110. In the laser resonator, a Ti:Al2 O3 laser crystal 14 as a tunable laser and a photoacoustic optical crystal 100 as a crystal for wavelength selection are arranged in the direction from the output side mirror 112 to the total reflection mirror 110. Thereby, an output light of wide range wavelength band, which is outputted from the laser crystal 14 and made to enter the photoacoustic optical crystal 100, is diffracted in a specified direction and outputted from the photoacoustic optical crystal 100 as diffraction light 106. Only the diffraction light 106 is reflected with the total reflection mirror 110 and reciprocates in the laser resonator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for selecting a wavelength in a tunable laser and a laser oscillating device capable of selecting a wavelength in a tunable laser. The present invention relates to a method for selecting a wavelength in a tunable laser that can be controlled, and a laser oscillation device capable of selecting a wavelength in a tunable laser.

[0002]

BACKGROUND OF THE INVENTION As a wavelength tunable laser, Ti: Al is used as a laser medium.
_A solid laser using a crystal such as ₂ O ₃ (titanium sapphire) and a liquid laser using a dye solution or the like as a laser medium are widely used.

Conventionally, as a wavelength selection method for causing such a wavelength tunable laser to oscillate at a desired wavelength, for example, a diffraction grating or a birefringent plate is provided in a laser resonator containing a wavelength tunable laser medium. By mechanically rotating such a diffraction grating or birefringent plate, only the emission light of a desired wavelength is extracted from the emission light emitted from the wavelength tunable laser, and the extracted emission light is applied to the wavelength tunable laser. There is known a wavelength selection method in which laser light is reflected and amplified to generate laser oscillation, and only laser light having a desired wavelength is emitted from a laser resonator.

However, in the case where the above-mentioned conventional wavelength selection method is used, it is difficult to increase the wavelength variable speed because the diffraction grating and the birefringent plate are mechanically rotated. To increase the wavelength reproduction accuracy,
There is a problem that the wavelength can be swept only in one direction.

As a means for solving such a problem, Taylor et al. Proposed an electric wavelength sweep method of a pulse dye laser (reference: APPL).
IED PHYSICS LETTERS, VOLU
ME 19, NUMBER 8, 15 OCTOBE
R 1971, pp. 269-271 "Electro
nic Tuning of Dye Laser U
sing theAcousto-Optical Fil
ter. " J. Taylor, S.M. E. FIG. Har
ris, S.M. T. K. Nieh and T.S. W. H
ansch).

The electrical wavelength sweeping method of the pulsed dye laser proposed by Taylor et al. Arranges a CaMoO ₄ crystal in a dye solution which is a laser medium.
An acoustic wave is input to the oO ₄ crystal, and a resonator is formed by light components interacting with the acoustic wave to vary the oscillation wavelength of the laser.

However, the electrical wavelength sweep method of the pulse dye laser proposed by Taylor et al. (1) has a narrow wavelength range that can be varied.

(2) A complicated structure for integrating the dye and the crystal is required.

(3) A special crystal called CaMoO ₄ crystal is required.

(4) Since the difference between the interacting light component and the non-interacting light component is the rotation of the polarization plane, separation is not easy. There were problems such as.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned various problems of the prior art, and has as its object to provide a method without providing a mechanically movable portion such as a rotating mechanism. By controlling the laser wavelength electrically and sweeping the wavelength at high speed, the whole device is downsized, and the widely used reliable photoacoustic optical crystal is used as an independent component for stable operation. An object of the present invention is to provide a wavelength selection method for a wavelength tunable laser and a laser oscillation device capable of wavelength selection in a wavelength tunable laser so as to realize a wavelength selection function.

[0012]

In order to achieve the above object, a method of selecting a wavelength in a tunable laser and a laser oscillating device capable of selecting a wavelength in the tunable laser according to the present invention include conventional diffraction gratings and birefringent plates. This is done from a completely different point of view.

That is, when an acoustic wave is generated in a birefringent photoacoustic optical crystal such as a TeO ₂ crystal, diffraction of a specific wavelength corresponding to the frequency of the acoustic wave in light incident on the crystal. The polarization plane of the light is not only perpendicular to the polarization plane of the undiffracted light, but also focused on the point that the exit angle of the diffracted light is deviated so as to be significantly different from the exit angle of the undiffracted light. Things.

FIG. 1 is a conceptual diagram showing a wavelength selection effect using a polarization effect of light of a specific wavelength by an acoustic wave. In a photoacoustic optical crystal 100 having a birefringent property, a wavelength λ is included.
i, the incident light 102 having the angular frequency ωi is assumed to be incident. Further, when an acoustic wave 104 having a frequency ωa is applied to the photoacoustic optical crystal 100, diffracted light 106 is obtained.

As shown in FIG. 2, for example, a total reflection mirror 110 and an output side mirror 112 having a predetermined transmittance are arranged for the diffracted light 106 as a light ray component diffracted by the photoacoustic optical crystal 100. Then, the total reflection mirror 110
The diffracted light 106 passes between the two by the
The laser resonator which reciprocates is constructed. Here, the wavelength of the diffracted light 106 is determined by the frequency of the acoustic wave 104 generated in the photoacoustic optical crystal 100. When the acoustic wave 104 having a frequency corresponding to the distortion is input to the photoacoustic optical crystal 100 by attaching and driving the piezoelectric element by the RF power supply to generate distortion in the piezoelectric element, the frequency of the RF power supply , The variable control of the laser wavelength becomes possible.

Further, since the diffraction efficiency of the diffracted light 106 is determined by the intensity of the acoustic wave, the loss of the laser resonator can be controlled by controlling the input intensity of the RF power source, and hence the laser output can be variably controlled.

However, since the diffraction angle α 109 is not completely constant with respect to the wavelength of the diffracted light 106, the vertical reflection of the total reflection mirror 110 on the diffracted light 106 causes
The wavelength range in which a laser resonator can be formed is narrow, and in order to cause laser oscillation in a wide wavelength range, a total reflection mirror 110 is required.
Since the angle of arrangement must be adjusted little by little, there is a possibility that the adjustment work becomes complicated in practice. For this reason,
In order to widen the variable wavelength range without changing the arrangement angle of the total reflection mirror 110, the diffraction angle α
It is necessary to correct the blur at 109.

As a means for correcting the blur of the diffraction angle α109, for example, an optical element such as a triangular prism for dispersing the wavelength of light is used, and the blur angle Δα of the wavelengths λ1 and λ2 is used.
Can be set so as to travel almost parallel after passing through the triangular prism. Thereby, the diffracted light 10
6 can always be vertically incident on the total reflection mirror 110, and a laser resonator for a wide wavelength range can be configured.

Further, when the output intensity of the laser is increased and the photoacoustic optical crystal 100 in the laser resonator may be damaged by light (for example, when a TeO ₂ crystal is used as the photoacoustic optical crystal 100, Since the crystal damage threshold of the TeO ₂ crystal is smaller than the damage threshold of the laser crystal and the optical component, the crystal is easily damaged.) A magnifying means such as a beam magnifier such as a telescope for enlarging a beam diameter is arranged, and
Can be reduced.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a wavelength selecting method in a wavelength tunable laser and a wavelength selectable laser oscillation device in a wavelength tunable laser according to the present invention will be described below in detail with reference to the accompanying drawings. .

FIG. 2 shows a wavelength-selectable laser oscillation device (hereinafter simply referred to as “laser oscillation device”) in a wavelength-tunable laser for implementing the wavelength selection method in the wavelength-tunable laser according to the first embodiment of the present invention. ) Is shown. The same components as those shown in FIG. 1 are denoted by the same reference numerals for easy understanding.

In this laser oscillation device, the emission side mirror 112 and the total reflection mirror 11 having a predetermined transmittance are provided.
0 forms a laser resonator.

In the laser resonator, a Ti: Al ₂ O ₃ laser crystal 14 as a wavelength tunable laser and a photoacoustic optical crystal 100 as a wavelength selecting crystal are arranged from the output side mirror 112 side to the total reflection mirror 110. It is arranged in order toward the side.

A piezoelectric element 22 driven by an RF power supply 20 is attached to the photoacoustic optical crystal 100 as acoustic wave input means. Accordingly, when the piezoelectric element 22 is driven by the RF power source 20 to cause distortion in the piezoelectric element 22, an acoustic wave having a frequency corresponding to the distortion is generated in the photoacoustic optical crystal 100 based on the distortion of the piezoelectric element 22. Will be entered.

The total reflection mirror 110 reflects the diffracted light 10 diffracted in a predetermined direction by the photoacoustic optical crystal 100.
It is configured to reflect only 6.

The piezoelectric element 22 is configured to input an acoustic wave to the photoacoustic optical crystal 100 so as to diffract only light having the wavelength of the emitted laser light to be emitted from the emission side mirror 112.

In the above configuration, the excitation laser light 24
Using the second harmonic of the Nd: YAG laser as T
i: Excite the Al ₂ O ₃ laser crystal 14. Further, based on the above-described principle, the frequency of the RF power supply 20 is controlled according to the wavelength of the emission laser light to be emitted from the emission mirror 112, and the piezoelectric element 22 is driven.

As described above, the photoacoustic optical crystal 10
In the outgoing light of a wide wavelength band emitted from the Ti: Al ₂ O ₃ laser crystal 14 incident on the
The outgoing light having a wavelength corresponding to the frequency of 0 is diffracted in a predetermined direction and becomes the diffracted light 106 as the photoacoustic optical crystal 10.
It will be emitted from 0. Thus, only the diffracted light 106 diffracted in the predetermined direction emitted from the photoacoustic optical crystal 100 is reflected by the total reflection mirror 110,
It will reciprocate in the laser resonator.

Therefore, only light having a wavelength corresponding to the frequency of the RF power supply 20 is amplified to cause laser oscillation, and only laser light of the wavelength is emitted from the laser resonator.

FIG. 3 is a schematic diagram showing the configuration of a laser oscillation device according to a second embodiment of the present invention. In addition, the same components as those shown in FIGS. 1 and 2 are denoted by the same reference numerals for easy understanding.

In the laser oscillating device according to the second embodiment, similarly to the laser oscillating device according to the first embodiment, the output mirror 112 having a predetermined transmittance is used.
And a total reflection mirror 110 constitute a laser resonator.

In the laser resonator, a Ti: Al ₂ O ₃ laser crystal 14, a photoacoustic optical crystal 100, and a diffraction light correcting prism 28 are sequentially arranged from the exit mirror 112 side to the total reflection mirror 110 side. It is arranged.

The diffracted light correcting prism 28 is configured to always emit the diffracted light 106 emitted from the photoacoustic optical crystal 100 in a fixed direction regardless of the wavelength.
The total reflection mirror 110 is configured to reflect light emitted from the diffraction light correction prism 28.

In the same manner as in the first embodiment, the piezoelectric element 22 emits light such that only the output light having the wavelength of the output laser light to be output from the output side mirror 112 is diffracted in a predetermined direction. It is configured to input an acoustic wave to the acousto-optic crystal 100.

In the above configuration, the excitation laser light 24
Using the second harmonic of the Nd: YAG laser as T
i: Excite the Al ₂ O ₃ laser crystal 14. Further, based on the principle described above, the frequency of the RF power supply 20 is controlled in accordance with the wavelength of the emitted laser light to be emitted from the emission side mirror 112, and the piezoelectric element 22 is driven.

As described above, the photoacoustic optical crystal 10
In the outgoing light of a wide wavelength band emitted from the Ti: Al ₂ O ₃ laser crystal 14 incident on the
The outgoing light having a wavelength corresponding to the frequency of 0 is diffracted in a predetermined direction and becomes the diffracted light 106 as the photoacoustic optical crystal 10.
It will be emitted from 0. Further, the diffracted light 1 diffracted in a predetermined direction from the photoacoustic optical crystal 100 and emitted.
06 enters the diffraction light correction prism 28 and is emitted in a certain direction. Then, the diffraction light correcting prism 28
Is reflected by the total reflection mirror 110 and reciprocates in the laser resonator.

Therefore, only light having a wavelength corresponding to the frequency of the RF power supply 20 is amplified to generate laser oscillation, and only laser light having the wavelength is emitted from the laser resonator.

FIG. 4 is a schematic diagram showing the configuration of a laser oscillation device according to a third embodiment of the present invention. Note that the same components as those shown in FIGS. 1, 2, and 3 are denoted by the same reference numerals for easy understanding. In the laser oscillation device according to the third embodiment as well, similarly to the laser oscillation device according to the second embodiment, a laser resonator is constituted by the emission side mirror 112 having a predetermined transmittance and the total reflection mirror 110. Have been.

In the laser resonator, a Ti: Al ₂ O ₃ laser crystal 14 and a telescope 30 for adjusting the beam diameter are used.
, Photoacoustic optical crystal 100, and diffraction light correcting prism 2
8 are sequentially arranged from the exit side mirror 112 side to the total reflection mirror 110 side.

Here, the telescope 30 is configured so that the beam diameter of light incident on the photoacoustic optical crystal 100 can be enlarged to a desired size.

Here, similarly to the second embodiment, the diffracted light correcting prism 28 is configured to always emit the light emitted from the photoacoustic optical crystal 100 in a fixed direction regardless of the wavelength. The total reflection mirror 110 is configured to reflect the light emitted from the diffraction light correcting prism 28. Further, the piezoelectric element 22 is configured to input an acoustic wave to the photoacoustic optical crystal 100 so that only the outgoing light having the wavelength of the outgoing laser light to be emitted from the outgoing side mirror 112 is diffracted in a predetermined direction. Have been.

In the above configuration, the excitation laser light 24
Using the second harmonic of the Nd: YAG laser as T
i: Excite the Al ₂ O ₃ laser crystal 14. Further, based on the above-described principle, the frequency of the RF power supply 20 is controlled according to the wavelength of the emission laser light to be emitted from the emission mirror 112, and the piezoelectric element 22 is driven.

As described above, the light emitted from the Ti: Al ₂ O ₃ laser crystal 14 in a wide wavelength band is expanded to a desired size by the telescope 30 and the photoacoustic The light will be incident on the optical crystal 100.

Therefore, even when the output intensity of the laser increases, the photoacoustic optical crystal 1
00, the beam diameter of the light incident on the photoacoustic crystal 100 is enlarged.
Since the output intensity per unit area of 0 is reduced, damage to the photoacoustic optical crystal 100 can be suppressed.

In the light emitted from the Ti: Al ₂ O ₃ laser crystal 14 through the telescope 30 and emitted from the Ti: Al ₂ O ₃ laser crystal 14, the frequency of the RF The outgoing light of the corresponding wavelength is diffracted in a predetermined direction and is emitted from the photoacoustic optical crystal 100 as the diffracted light 106. further,
The diffracted light 106 diffracted and emitted from the photoacoustic optical crystal 100 in a predetermined direction is incident on the diffraction light correcting prism 28 and is emitted in a certain direction. The light emitted from the diffraction light correcting prism 28 is reflected by the total reflection mirror 11.
It will be reflected by zero and will reciprocate in the laser resonator.

Therefore, only the light having the wavelength corresponding to the frequency of the RF power supply 20 is amplified to generate laser oscillation, and only the emitted laser light of the wavelength can be emitted from the laser resonator.

FIG. 5 is a graph showing the result of an experiment using the laser oscillation apparatus shown in FIG. 2 according to the first embodiment under the following experimental conditions, in which the frequency of the RF power supply 20 was changed. The relationship between the output of the emitted laser light and the wavelength at that time is shown. As is clear from the experimental results shown in FIG. 5, when the laser oscillation device shown in the first embodiment is used, an arbitrary wavelength is selected to perform laser oscillation in a wavelength range of about 800 nm to about 811 nm. be able to.

(FIG. 5: Experimental Conditions) Excitation laser light 24: Second harmonic of Nd: YAG laser (pulse laser) Wavelength 532 nm, Energy 155 mJ / pulse, Pulse width 8 ns Emitting mirror 112: 60% reflection Total reflection Mirror 110: 99.9% reflection at a wavelength of 800 nm RF power supply 20: Frequency variable range 40 MHz to 150 MHz Input power 0 W to 1 W Photoacoustic optical crystal 100: 98% diffraction efficiency FIG. 6 shows the third embodiment shown in FIG. FIG. 10 is a graph showing the results of an experiment performed under the following experimental conditions using the laser oscillation device shown in FIG. 1 and showing the relationship between the output of the output laser light and the wavelength when the frequency of the RF power supply 20 was changed. I have. As is clear from the experimental results shown in FIG. 6, the wavelengths of about 750 nm to about 850 nm can be obtained by using the laser oscillation devices shown in the second and third embodiments.
In this wavelength range, an arbitrary wavelength can be selected to perform laser oscillation.

(FIG. 6: Experimental Conditions) Excitation laser light 24: Second harmonic of Nd: YAG laser (pulse laser) Wavelength 532 nm, energy 155 mJ / pulse, pulse width 8 ns Emitting mirror 112: 60% reflection Total reflection Mirror 110: 99.9% reflection at a wavelength of 800 nm RF power supply 20: Frequency variable range 40 MHz to 150 MHz Input power 0 W to 1 W Photoacoustic optical crystal 100: Diffraction efficiency 98% Further, FIG. 7 shows the second embodiment shown in FIG. 3 shows a change in output of the emitted laser light when the intensity of the acoustic wave 104 input to the photoacoustic optical element 100 is changed using the laser oscillation device described in the first embodiment. As is clear from the experimental results shown in FIG. 7, when the laser oscillation device according to the second embodiment is used, the intensity of the acoustic wave 104 input to the photoacoustic optical element 100 is 0.5 W to 2.0 W. , The output of the emitted laser light also changes accordingly, so that the acoustic wave 104 input to the photoacoustic optical element 100 is changed.
By changing the intensity of the laser beam, the output of the emitted laser light can be changed.

In each of the above embodiments, the case of pulse excitation using a Ti: Al ₂ O ₃ laser crystal as a laser medium has been described. However, the present invention is not limited to this. Needless to say, the present invention can also be used for other wavelength tunable lasers such as a liquid laser using such a method and a continuous light excitation type laser.

[0051]

Since the present invention is configured as described above, it is possible to select the wavelength of the emitted laser light without providing a mechanically movable part such as a rotating mechanism, so that the entire apparatus can be selected. The size can be reduced, and a stable wavelength selecting action can be realized.

That is, since the laser wavelength is controlled electrically and the wavelength is swept at a high speed without providing a mechanically movable part such as a rotating mechanism, the size of the entire apparatus can be reduced. As a result, since a widely used highly reliable photoacoustic optical crystal can be used as an independent component, a stable wavelength selection action can be realized.

Further, by using an optical element such as a prism for correcting a diffracted light, which corrects the deflection angle of the diffracted light, it becomes possible to emit the emitted laser light in a wide wavelength range.

Furthermore, if an expanding means for controlling the beam diameter of light incident on the photoacoustic optical crystal such as a telescope is used, the light incident on the photoacoustic optical crystal in the photoacoustic optical crystal can be reduced. Since the light intensity per unit area can be reduced, high output laser light can be realized while suppressing damage to the photoacoustic optical crystal.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a wavelength selection operation using a diffraction operation of light of a specific wavelength by an acoustic wave.

FIG. 2 is a schematic configuration explanatory view of a laser oscillator capable of selecting a wavelength in the wavelength tunable laser for performing the wavelength selection method in the wavelength tunable laser according to the first embodiment of the present invention.

FIG. 3 is a schematic configuration explanatory view of a wavelength-selectable laser oscillation device in a wavelength-tunable laser for performing a wavelength selection method in a wavelength-tunable laser according to a second embodiment of the present invention.

FIG. 4 is a schematic structural explanatory view of a wavelength selectable laser oscillation device in a wavelength tunable laser for implementing a wavelength selection method in a wavelength tunable laser according to a third embodiment of the present invention.

FIG. 5 is a graph showing a relationship between the output of the output laser light and the wavelength when the frequency of the RF power supply is changed in an experiment using the laser oscillation device shown in the first embodiment.

FIG. 6 is a graph showing the relationship between the output laser light output and the wavelength when the frequency of the RF power supply is changed in an experiment using the laser oscillation device shown in the second embodiment.

FIG. 7 shows a change in output of emitted laser light when the intensity of an acoustic wave input to a photoacoustic optical element is changed in an experiment using the laser oscillation device shown in the second embodiment. It is a graph.

[Explanation of symbols]

Reference Signs List 14 Ti: Al ₂ O ₃ laser crystal 20 RF power supply 22 Piezoelectric element 24 Excitation laser light 28 Diffractive light correcting prism 30 Telescope 100 Photoacoustic optical crystal 102 Incident light 104 Acoustic wave 106 Diffracted light 108 Non-diffracted light 109 Diffraction angle α 110 Total reflection mirror 112 Output side mirror

Claims (7)

[Claims] 1. A crystal to which an acoustic wave is input is arranged in a laser resonator, and a tunable laser capable of oscillating laser light in a predetermined wavelength range is incident on the crystal, and a wavelength is set according to the frequency of the acoustic wave. In the wavelength selection method for controlling, a birefringent photoacoustic optical crystal is used as the crystal, and a laser resonator is configured only for a light component diffracted in a specific direction by the photoacoustic optical crystal. A wavelength selection method for a tunable laser. 2. The wavelength selecting method for a wavelength tunable laser according to claim 1, wherein a variation of a diffraction angle according to a wavelength of a light component diffracted in a specific direction by the photoacoustic optical crystal is determined by using a wavelength dispersive optical element. A wavelength selecting method for a wavelength tunable laser, wherein the wavelength is corrected. 3. The wavelength selecting method in the wavelength tunable laser according to claim 1, wherein a beam diameter of light incident on the photoacoustic optical crystal is increased,
A wavelength selecting method for a wavelength tunable laser, wherein damage to the photoacoustic optical crystal is suppressed. 4. The wavelength selecting method according to claim 1, wherein the laser output is controlled by changing the intensity of an acoustic wave input to the photoacoustic optical element. A wavelength selecting method for a wavelength tunable laser, comprising: 5. A laser resonator constituted by opposed mirrors having a predetermined reflectance, a tunable laser medium oscillated in a predetermined wavelength range provided in the laser resonator, and a tunable laser medium; A photoacoustic optical crystal disposed in a laser resonator, to which light emitted from the tunable laser medium is incident; and a photoacoustic optical crystal mounted on the photoacoustic optical crystal for inputting an acoustic wave to the photoacoustic optical crystal. A wavelength selectable laser oscillation device for a wavelength tunable laser, comprising: an acoustic wave input unit. 6. A laser resonator constituted by opposed mirrors having a predetermined reflectance, a tunable laser medium capable of oscillating laser in a predetermined wavelength range provided in the laser resonator, A photoacoustic optical crystal disposed in a laser resonator, to which light emitted from the tunable laser medium is incident; and a photoacoustic optical crystal mounted on the photoacoustic optical crystal for inputting an acoustic wave to the photoacoustic optical crystal. A wavelength selectable wavelength tunable laser comprising: an acoustic wave input unit; and an optical element disposed in the laser resonator and configured to correct a deflection angle of diffracted light emitted from the photoacoustic optical crystal. Laser oscillation device. 7. The laser oscillation device according to claim 5, wherein the wavelength-selectable laser is provided in the laser resonator and is incident on the photoacoustic optical crystal. A wavelength-selectable laser oscillation device for a wavelength-variable laser, comprising: an expanding means for expanding a beam diameter of light emitted from the wavelength-variable laser medium.